Thomas Joseph Kelly was an Irish revolutionary and leader of the Irish Republican Brotherhood (IRB), a secret organisation with the objective of establishing an Irish republic independent from the United Kingdom. Kelly was the nominal leader of the failed Fenian Rising of 1867. He had previously also been an officer in the Union Army during the American Civil War, serving mainly with the 10th Ohio Infantry "The Bloody 10th".

The Irish Republican Brotherhood was a secret oath-bound fraternal organisation dedicated to the establishment of an "independent democratic republic" in Ireland between 1858 and 1924. Its counterpart in the United States of America was initially the Fenian Brotherhood, but from the 1870s it was Clan na Gael. The members of both wings of the movement are often referred to as "Fenians". The IRB played an important role in the history of Ireland, as the chief advocate of republicanism during the campaign for Ireland's independence from the United Kingdom, successor to movements such as the United Irishmen of the 1790s and the Young Irelanders of the 1840s.